Robert M. Owens

A trilobite fauna from the highest Shineton Shales in Shropshire, and the correlation of the latest Tremadoc

A rich fauna dominated by trilobites and calcified chordates has been collected in Shropshire from the Arenaceous Beds, the highest member of the Tremadoc Shineton Shale Formation, and hitherto regarded as poorly fossiliferous. This fauna shows that shelf conditions persisted longer in Shropshire than has been supposed. It is likely that even younger Tremadoc is cut out at the unconformity below the Caradoc in the Shineton Inlier. The correlation of the later Tremadoc is reviewed, and the nomenclature of British Tremadoc biozones is revised. The trilobites described here are a mixture of previously known and new forms. The name Shumardia (Conophrys) salopiensis Callaway is revived for British material traditionally assigned to the Scandinavian species Shumardia pusilla (Sars), from which it is distinct. The new taxa Litagnostus meniscus sp.nov., Apatokephalus sarculum sp.nov. and Skljarella cracens sp.nov. are described. The type species of Asaphellus, A. homfrayi and Leptoplastides, L. salteri , are redescribed, and Geragnostus callavei, Pseudokainella impar , and Parapilekia sp. are recorded. New information on the ontogeny of S. (C.) salopiensis and A. homfrayi is given. Litagnostus and Skljarella are recorded from the British Isles for the first time.

Proetide trilobites from the Cystoid Limestone (Ashgill) of NW Spain, and the suprageneric classification of related forms

KurzfassungNur wenige Trilobiten der Ordnung Proetida wurden bisher aus der ordovizischen»Selenopeltis Provinz« gemeldet. Im folgenden werden vier Arten aus dem Cystoideen-Kalk, Ashgill, der östlichen Iberischen Ketten NW-Spaniens beschrieben und den GattungenRadnoria, Harpidella, Panar- chaeogonus undRorringtonia zugerechnet. Zwei Arten,Radnoria carlsi undRorringtonia lenis, sind neu, die übrigen Arten werden in offener Nomenklatur belassen. Im Anhang wird die Klassifikation der|enigen Proetida besprochen, die zu den Aulacopleuridae, Brachymetopidae und der neuen Familie Rorringtoniidae gehören. Sie alle werden in die Superfamilie Aulacopleuracea gestellt.AbstractFew trilobites of the Order Proetida have been reported from the Ordovician»Selenopeltis Province«. Herein four species from the Ashgill Cystoid Limestone of the eastern Iberian Chains, NW Spain, are described and assigned to the generaRadnoria, Harpidella, Panarchaeogonus andRorringtonia. Two species,Radnoria carlsi andRorringtonia lenis, are new, and the others are described under open nomenclature. In the appendix, classification of Proetida belonging to the Aulacopleuridae, Brachymetopidae and the new family Rorringtoniidae is discussed, and all are included in the superfamily Aulacopleuracea.

The palaeogeographic position of the Lake District in the Early Ordovician

The early Ordovician was a time of maximum continental separation and hence a time when faunal evidence can be used to assess palaeogeography in a critical way. We summarize the known trilobite occurrences (18 genera) from the Arenig–Llanvirn of the Lake District, and record some genera for the first time. Maps of the distribution of some of these forms are given. All genera except Cyclopyge were confined to the Gondwana continent at the time, and some are known from many localities; and two species are widespread in England, Wales, France, Iberia and Bohemia. The fauna is entirely distinct from those of Scandinavia and North America. All the palaeontological evidence points to the Lake District being adjacent to Ordovician Gondwana. In the earlier Ordovician it is not reasonable to suggest that the Iapetus Ocean lay to the south of the Lake District as did Allen (1987).

Lower Cambrian fossils from the Hell’s Mouth Grits, St Tudwal’s Peninsula, North Wales

The trilobites Hamatolenus (Myopsolenus) douglasi sp. nov., Kerberodiscus succinctus gen. et sp. nov. and Serrodiscus ctenoa? Rushton, 1966 are described from the upper part of the Hell’s Mouth Grits, St Tudwal’s Peninsula, together with hexactinellid sponge spicules, trace fossils and a single inarticulate brachiopod. The fauna is of late lower Cambrian age, within the upper part of the protolenid-strenuellid Zone of the Comley Series of British nomenclature. From comparison with related faunas the horizon is correlated approximately with beds in New York State containing the Acimetopus faunule, the top of the Issafénien Stage of Morocco, and the uppermost lower Cambrian trilobite-bearing horizon in the Purley Shales of Warwickshire, but it is younger than the Pseudatops viola horizon in the Llanberis Slates. The top of the Hell’s Mouth Grits is lithologically equivalent to the uppermost Rhinog Grits of the Harlech Dome. Smooth (effaced) eodiscid trilobites are shown to be polyphyletic, and to complement the evidence of the Hell’s Mouth eodiscids Runcinodiscus index gen. et sp. nov. is described from the lower Cambrian of Comley, Salop.

Newly discovered Tremadoc rocks in the Carmarthen District, South Wales

Newly discovered Tremadoc rocks in South Wales are described from outcrops south of Carmarthen. The faunas suggest that both the Clonograptus tenellus and Shumardia pusilla Zones are represented, together with possible higher Tremadoc strata.

The Habberley Formation: youngest Tremadoc in the Welsh Borderlands

The Habberley Formation overlies the Shineton Shale Formation in the Shelve Inlier, Shropshire, and includes the youngest Tremadoc strata known from the Welsh Basin. It probably represents deposition during the interval cut out by the sub-Arenig unconformity in North Wales, and removed by the sub-Caradoc unconformity in the Wrekin district. There is no angular unconformity between Tremadoc and Arenig in the Shelve Inlier. The Habberley Formation is likely to correlate in part with the Hunnebergian Stage of Scandinavia. It was deposited probably in a largely stagnant basin, and records a shallowing-upwards sequence, prior to the Arenig transgression of the Stiperstones Quartzite. A sparse trilobite fauna proves the presence of the Angelina sedg vickii Biozone, and a succeeding interval is characterized by Asaphellus cf. graffi . The trilobites are briefly described; they include the first undistorted material of Angelina sedgwvickii . The brachiopod Lingulella bella (Walcott), hitherto known only from eastern Newfoundland, is described by A. W. A. Rushton.

Long-period orbital climate forcing in the early Palaeozoic?

Facies indicators and geochemical proxies of early Palaeozoic global climate cooling suggest episodes of fluctuating glacio-eustasy and severe cold or glaciation from the Mid–Late Cambrian to Silurian (c. 85 myr), with a mean frequency of 2.6 myr. Long-period orbital time series predicted through the Phanerozoic are used to generate sine waves to test against these data; the null hypothesis of no orbital influence is rejected with a high confidence level. Cooling episodes appear most frequent through the Late Ordovician leading up to the Hirnantian glacial maximum, but even ‘greenhouse’ intervals of the Early–Mid-Ordovician and early Silurian provide evidence for periodic cooling episodes.

Arenig biostratigraphy and correlation in the Welsh Basin

Recent work on the Arenig Series in the Welsh Basin is reviewed; it is now known to be far more complete and richly fossiliferous than has been supposed. Three regional stages, Moridunain, Whitlandian and Fennian, and seven trilobite-based biozones have been defined. Outstanding problems are highlighted, among which remains the definition of a stratotype for a base for the series, for which there appears to be only one feasible candidate in this area, in the Shelve inlier.

Pseudoextinctions in late Devonian proetide trilobites

Morphologically similar proetide trilobite genera occur in highest Devonian or lowest Carboniferous and in Middle Devonian strata, but are absent from the intervening Upper Devonian. The similarities have been accounted for either by true phyletic relationship, or by homoeomorphy. Genera from four proetide lineages are discussed, and it is concluded that these underwent ‘pseudoextinction’ in the Upper Devonian, presumably surviving in refugia of limited spatial extent that have not been preserved in the geological record.

Late Ordovician trilobites from the Karagach Formation of the western Tarbagatai Range, Kazakhstan

Two trilobite faunas of late Ordovician (Sandbian and Katian) age are described from the siliciclastic Karagach Formation, western Tarbagatai Range, eastern Kazakhstan. They comprise 15 families and 24 genera and include the new taxa Agerina acutilimbata sp. nov., Birmanites akchiensis sp. nov., Dulanaspis karagachensis sp. nov. and Kimakaspis kovalevskyi gen. et sp. nov. Most of the Karagach Formation yields graptolites characteristic of the Diplograptus foliaceus [ multidens ] Biozone, which are associated with the older trilobite fauna; the uppermost part, which is the source of the younger trilobite fauna, contains Orthograptus quadrimucronatus and Dicranograptus hians which suggest a younger age, equating with the lowermost Ensigraptus caudatus Biozone, and the base of the Katian Stage. Most of the trilobite genera in both faunas have a wide geographical distribution in the late Ordovician, although Dulanaspis and Sinocybele are characteristic of low latitude eastern peri-Gondwanan faunas.